Overview on Physical Cosmology
Lead: Eberhard Möbius

2/6/2006

Summary by Sam Schweizer

Reading Material

Ferris, The Whole Shebang; Ch. 1,2,4,6;
Ben-Ari “Just a Theory”, Ch. 1;
"Curtains of the Universe", Astronomy, March 95;
“Absurd Universe”, Astronomy, Nov 03 (PDFs in Blackboard);
Lecture Notes (www);

The class lecture started out with an introduction from Eberhard Möbius and an explanation of the grading system. The class then discussed why each member was taking Cosmology. The general consensus was that everyone wanted to learn more about Cosmology. No one had to take the class and there were many observers who were not even enrolled.

People didn’t want to know just about our physical world however. Some wanted answers to those big why questions. Why are we here? What does it all mean? What happened before the big bang (if the big bang did occur)?

People come to the class from a variety of backgrounds as well. I, the author, come from the business school, but there are representatives from many of the colleges at the University of New Hampshire.

The main discussion was proctored by Professor Möbius and was an overview on physical cosmology. Professor Möbius had a Powerpoint presentation sprinkled with amusing illustrations of his points. The presentation started out with some questions:

• How does the universe “tick?”
• What is behind the wall (the edge of our known universe)?
• Is studying our universe like the Escher painting The Gallery where we look out into the cosmos and end up staring right back at ourselves?
• How do we really study something that we are part of?

Professor Möbius continued with some problems of cosmology and a few facts as well. Cosmology, Möbius conceded, is a very “tough and unusual” for science to handle. We can not make observations on other universes because there is only one. Professor Möbius also mentioned that there is some debate as to whether there is more than one universe but it didn’t concern the class yet. What creates problems for cosmologists, as well, is that we are really restricted to our observable universe. Since light only travels so fast, and since the universe originated 13.7 billion years ago, we can only observe about 13.7 billion light years in any direction. Although that’s a long way, it may not be the edge.

However, there is a problem with thinking of the universe as being infinite. A physician named Olbers, who was a hobby-astronomer, came up with this strange paradox. If stars are evenly spaced, and the universe is infinite, then why is the night sky not filled with stars so much that it is blindingly light?

Red Shift explains that light moving away from an observer is shifted towards the red end of the visible spectrum. Edwin Hubble found that the farther away a galaxy is, the stronger the Red Shift in its spectral lines. Something interesting to note is that the Hubble theory is correct, but the constant has changed as our measuring instruments have become more precise. On a more theoretical note, if the space between us and a light emitting object is expanding so fast that the object recedes from us faster than the speed of light, we would not be able to see it.

An important observation has been that objects all around us are shifting towards red. This means that the universe is expanding. If the universe is expanding then it must have been bunched-up at one point; hence, the Big Bang theory!

Professor Möbius also discussed how we measure things in astronomy. We measure distances by measuring parallax. This can be simulated very easily be holding your thumb 6” from your face. When you open one eye at a time, your thumb shifts drastically from one side to the other. When you hold out your thumb at arm’s length, the shift is much less. This basic principle allows us to measure how far away other planets are.

One astronomical unit is the distance from the Earth to the Sun. The closest star to us (other than the Sun) is Alpha Centauri which is four light years away! To put this all into perspective, if the sun was 6” in diameter, the earth would be the size of the head of a needle. With a 6” inch Sun in Durham NH, Alpha Centauri would be in San Francisco. Even if there are other forms of life in the cosmos, we are at the moment, very alone in space.

The general discussion for the class was very interesting. Dark Energy was brought up and we discussed that no one really knows what it is but it may have a severe impact on how our universe operates. The thought that space can expand faster than the speed of light was also discussed but many class members still did not really know what that meant by the end of class. Professor Möbius used the analogy of a balloon with two pennies attached to it. The surface of the balloon is space and when the balloon inflates the “distance” between the two points increases without them moving farther apart. How this works is out of the reach of this author’s conception.

An important distinction was discussed during the class as well. The description that Professor Möbius gave was a scientific-based description so it can’t look at things that we can’t observe. Things that function by essentially magic are only talked about outside of physical cosmology.